1. Field of the Invention
The present invention relates, in general, to a reception antenna structure of a tire pressure monitoring system and, more particularly, to a reception antenna of a tire pressure monitoring system using a radiating leakage coaxial cable, in which the reception antenna of the tire pressure monitoring system is implemented using the radiating leakage coaxial cable, thus further improving reception performance for measured data transmitted in a wireless manner, when a transmitter transmits tire pressure data measured by a temperature and pressure sensor included in the transmitter within a tire in a wireless manner. Korean application number 10-2003-0075734 filed Oct. 29, 2003 is hereby incorporated by reference.
2. Description of the Related Art
As well known to those skilled in the art, a tire pressure monitoring system (TPMS) used in automobiles includes a sensor 1 for measuring the internal temperature and pressure of a tire, a transmitter 2 for modulating data measured by the sensor 1 into data in an Ultra High Frequency (UHF) band, and transmitting the modulated data to the outside of the tire in a wireless manner, a receiver 3 for receiving the measured data transmitted from the transmitter 2 in a wireless manner, and a display unit 4 for displaying the measured data received by the receiver 3 on a liquid crystal display (LCD) screen to allow a driver to monitor the measured data, as shown in FIG. 1.
In this case, the sensor 1 and the transmitter 2 are installed within the tire, and the receiver 3 and the display unit 4 are installed outside of the tire.
In this way, in the case where the sensor 1 installed within the tire measures the temperature and pressure of the tire, the tire pressure monitoring system is operated so that measured temperature and pressure data for the tire are transmitted to the receiver 3 installed outside of the tire in a wireless manner through the transmitter 2, the receiver 3 transmits the received data to the display unit 4, and then the display unit 4 displays the measured data, such as the tire pressure and temperature, on the LCD screen.
At this time, the tire pressure monitoring system must guarantee reliability and stability in the characteristics thereof. Therefore, the tire pressure monitoring system is equipped with a reception antenna having a wireless interface function of enabling the measured data to be exactly received from the sensor 1. In this case, wavelength/4 (λ/4) monopole antennas 5 and 5′ are mainly used as the reception antenna, as shown in FIG. 1.
However, for the typical monopole antennas 5 and 5′, the reception characteristics thereof are influenced by the electromagnetic characteristics according to the materials, constructions, sizes and designs of automobiles. Therefore, in the prior art, the reception sensitivities of the monopole antennas 5 and 5′ differ according to the constructions, sizes and designs of automobiles as well as the materials thereof, so that the monopole antennas 5 and 5′ cannot satisfy standard criteria.
Therefore, in the prior art, a method of changing the position of the monopole antennas 5 and 5′ or arranging two or more λ/4 monopole antennas 5 and 5′ at suitable positions is used so as to improve the reception sensitivities of the antennas.
However, the above method is problematic in that, as the size of an automobile and the number of tires are increased, great efforts are required to estimate the optimal positions of the monopole antennas 5 and 5′, thus increasing the economic load due to the increased number of the monopole antennas.
Moreover, the above method is disadvantageous in that, since metal parts of the monopole antennas 5 and 5′ are consistently exposed to external environments, the monopole antennas 5 and 5′ are easily deformed or corroded due to the external factors, such as moisture and dust, as well as external physical impacts, thus the lifespan of the antennas is shortened.
For example, if the reception sensitivities of λ/4 monopole antennas are measured after the monopole antennas are applied to a truck equipped with 10 tires, it can be seen that the reception sensitivities for data measured at the monopole antennas are remarkably decreased, and deviations between measured data respectively obtained from the 10 tires are excessively increased due to the decrease of the reception sensitivities, as shown in FIG. 2.